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ABCD is a cyclic quadrilateral in which AB is parallel to DC and AB is a diameter of the circle. Given ∠BED = 65°; calculate :

(i) ∠DAB,

(ii) ∠BDC.

ABCD is a cyclic quadrilateral in which AB is parallel to DC and AB is a diameter of the circle. Given ∠BED = 65°; calculate ∠DAB, ∠BDC. Circles, Concise Mathematics Solutions ICSE Class 10.

Circles

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Answer

(i) We know that,

Angles in same segment are equal.

∴ ∠DAB = ∠BED = 65°.

Hence, ∠DAB = 65°.

(ii) We know that,

Angle in semi-circle is a right angle.

∴ ∠ADB = 90°.

In △ADB,

⇒ ∠ABD + ∠ADB + ∠DAB = 180°

⇒ ∠ABD + 90° + 65° = 180°

⇒ 155° + ∠ABD = 180°

⇒ ∠ABD = 180° - 155° = 25°.

As, AB || DC

∠BDC = ∠ABD = 25°.

Hence, ∠BDC = 25°.

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